update zlib version to 1.2.12 (#2106)

Author: waitingkuo

dev/docker/ballista-base.dockerfile

@@ -59,7 +59,7 @@ RUN echo "Building OpenSSL" && \
 
 RUN echo "Building zlib" && \
     cd /tmp && \
-    ZLIB_VERSION=1.2.11 && \
+    ZLIB_VERSION=1.2.12 && \
     curl -LO "http://zlib.net/zlib-$ZLIB_VERSION.tar.gz" && \
     tar xzf "zlib-$ZLIB_VERSION.tar.gz" && cd "zlib-$ZLIB_VERSION" && \
     CC=musl-gcc ./configure --static --prefix=/usr/local/musl && \
@@ -96,4 +96,4 @@ RUN cargo install cargo-build-deps
 
 # prepare toolchain
 RUN rustup update && \
-    rustup component add rustfmt
+    rustup component add rustfmt